Depositing an oxide

ABSTRACT

A dielectric deposited on a substrate may be exposed to a salt solution. While exposed to the salt solution, an oxide is deposited on the dielectric.

BACKGROUND

This invention relates generally to the fabrication of semiconductordevices and specifically to deposition techniques.

Incompatibilities between the metal and oxide layers inMetal-Oxide-Semiconductor or Metal-Oxide-Silicon (MOS) structures mayarise in those MOS structures having a dielectric with a high dielectricconstant (high-k) and a polysilicon or metal gate electrode. Forexample, a MOS structure having a high-k dielectric and a polysilicongate electrode may form nodules that may short the dielectric. Further,the nodules may pin the Fermi level in the polysilicon gate.Alternately, a MOS structure having a high-k dielectric and a metal gateelectrode may experience an undesirable shift in the gate metal workfunction. A shift in work function may lead to unstable thresholdvoltages thereby affecting device performance. As such, another oxidesuch as a buffer oxide may be deposited between the high-k dielectricand gate material.

Buffer oxides may be deposited on a substrate via chemical vapordeposition (CVD) processing techniques. For example, depositionprecursors may first be deposited on the substrate and then oxidized.However, some of the precursors used in the CVD of buffer oxide may behighly toxic and may spontaneously ignite and burn on contact with air.Thus, the CVD buffer oxide precursors pose a significant risk to thoseworking in the semiconductor industry. Further, unconsumed CVD processgases and deposition products may be as toxic as the starting materials.Thus, there is an additional hazard to the environment at large as aresult of CVD of buffer oxide.

Accordingly, there continues to be a need for deposition techniques thatare both environmentally and user friendly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a gate stack of a MOS structureaccording to some embodiments of the present invention;

FIG. 2 is a cross sectional view of the gate stack of FIG. 1 duringdevice fabrication;

FIG. 3 is a flow chart for the preparation of an oxide depositionsolution according to some embodiments of the present invention;

FIG. 4 is a flow chart for the deposition of oxide on the gate stack ofFIG. 2 according to some embodiments; and

FIG. 5 is a cross sectional view of the gate stack of FIG. 2 aftersoaking in the oxide deposition solution according to some embodimentsof the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1, according to some embodiments of the presentinvention, structure 10 such as a MOS structure as one example, mayinclude a substrate 12, a dielectric 14, a buffer oxide 16 and a gateelectrode 18. The substrate 12 may be any semiconducting material suchas silicon or gallium arsenide as a few examples. Further, thedielectric 14 may be an oxide such as silicon dioxide (SiO₂), hafniumoxide (HfO₂) or zirconia (ZrO₂) as a few examples. Generally, hafniumoxide and zirconia are considered high-k dielectrics because they havehigh electrical permittivity. The dielectric 14 may be very thin, forexample, 20 angstroms or less, although embodiments are not limited inthis respect. The gate electrode 18 may be any suitable gate materialsuch as a metal or polysilicon.

The buffer oxide 16 may be any oxide to buffer undesirable interactionsbetween the dielectric 14 and the gate material 18. For example, thebuffer oxide 16 may have a lower dielectric constant than the dielectric14. As such, the buffer oxide 16 may form a more stable interface with asubsequently deposited gate material 18 than the dielectric 14. Further,the buffer oxide 16 may react with the dielectric 14 to remove anypreexisting oxygen deficiencies or impurities and/or to passivate thedielectric 14 surface. Chemically, the buffer oxide 16 may be relativelystable, which buffers, or lessens the reactivity between the dielectric14 and the gate electrode 18. As such, adverse interactions between thedielectric 14 and gate 18 may be attenuated if not eliminated.Nevertheless, according to certain embodiments of the present invention,the oxide 16 is ultra-thin (although embodiments are not limited toultra-thin buffer oxide 16). In this way, overall gate stack capacitancemay not be compromised.

As described herein, the buffer oxide 16 is aluminum oxide (Al₂O₃) andthe dielectric 14 is hafnium oxide, although embodiments are not sorestricted. Generally, aluminum oxide is relatively stable and has alower dielectric constant than hafnium oxide. As such, aluminum oxidemay form a more stable interface with a subsequently deposited gate 18material.

Referring to FIG. 2, during device fabrication the substrate 12 may besilicon having hafnium oxide 14 deposited thereon. The hafnium oxide 14may be deposited on the substrate 12 by any conventional means such assputter deposition, CVD or high-density plasma CVD as a few examples.Thereafter, the substrate 12 may be immersed in an oxide depositionsolution according to embodiments of the present invention.

Referring to FIG. 3, according to embodiments of the present invention,buffer oxide 16 may be deposited on a dielectric 14 via surfacereactions while the substrate 12 is immersed in a “wet” oxide depositionor salt solution. For example, to deposit aluminum oxide 16 on thehafnium oxide 14, a salt such as an aluminum salt may be dissolved in asolvent, as shown in box 20. In some embodiments the aluminum salt maybe aluminum chloride or aluminum nitrate that is dissolved in deionizedwater.

As shown in box 22, the pH of the oxide deposition solution or saltsolution may be adjusted in some embodiments. For example, a base suchas ammonia hydroxide or an acid such as hydrochloric acid may be addedto the salt solution. In some embodiments of the present invention, thepH modifying substance may be added as process demands require such asto remove potential contaminants. Further, the pH modifying substancemay be utilized to dissolve any aluminum hydroxide precipitates orhydrate aluminum ions.

Referring to FIG. 4, after the oxide deposition solution has beenprepared, and when called for pH adjusted, the substrate 12 may bedipped in the solution, as shown in block 24. The substrate 12 may besoaked for about a few seconds to about an hour or more, althoughembodiments of the invention are not limited in this respect. Whilesoaking in the salt solution, reactants in the solution and the topsurface of the dielectric 14 may react to deposit the oxide 16 on thedielectric 14, as shown in block 26. For example, aluminum hydroxideAl(OH)₃ or hydrated aluminum ions may react with the top surface of thehafnium oxide 14 to form aluminum oxide 16. After being immersed for adesired period of time, the substrate 12 may be removed from the saltsolution and rinsed for example with deionized water, as shown block 28.

The thickness of the buffer oxide 16 deposited during substrate 12soaking may be controlled. For example, the thickness of the aluminumoxide 16 deposited on the hafnium oxide 14 may be regulated by adjustingthe concentration of aluminum salt dissolved in solvent and/or the timethe substrate 12 is allowed to soak in the salt solution. That is, insome embodiments of the present invention, the concentration of aluminumavailable for deposition may be about few parts per million (ppm) toabout 1 percent or 1 mole. Accordingly, the surface concentration ofaluminum oxide 16 may be modulated to range from about a few ppm or lessthan a complete layer to one or more atomic layers.

Referring to FIG. 5, as a result of exposure to the oxide depositionsolution, the oxide 16 may be deposited on the dielectric 14. Forexample, a desired thickness of aluminum oxide 16 may be deposited onhafnium oxide 14. Thereafter, a gate material 18 may be deposited on theoxide 16, as shown in FIG. 1.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

1. A method comprising: soaking a substrate having a dielectricdeposited thereon in a salt solutions said dielectric having a firstdielectric constant; and depositing an oxide on said dielectric, saidoxide having a second dielectric constant different from the firstdielectric constant.
 2. The method of claim 1 wherein depositing anoxide on said dielectric includes depositing primarily aluminum oxide onsaid dielectric.
 3. The method of claim 1 wherein soaking said substratein said salt solution includes soaking said substrate in a salt solutioncomprising an aluminum salt.
 4. The method of 3 wherein soaking saidsubstrate in said salt solution comprising said aluminum salt includessoaking said substrate in a salt solution comprising aluminum chloridedissolved in water.
 5. The method of 3 wherein soaking said substrate insaid salt solution comprising said aluminum salt includes soaking saidsubstrate in a salt solution comprising aluminum nitrate dissolved inwater.
 6. The method of claim 3 wherein soaking said substrate in saidsalt solution comprising said aluminum salt includes causing thereactants in said aluminum salt solution available for surface reactionto range from about a few parts per million to about one percent.
 7. Themethod of claim 1 wherein soaking said substrate in said salt solutionincludes adjusting the pH of said salt solution.
 8. The method of claim1 wherein depositing said oxide on said dielectric includes depositingsaid oxide on silicon dioxide.
 9. The method of claim 1 whereindepositing said oxide on said dielectric includes depositing said oxideon hafnium oxide.
 10. The method of claim 1 including depositing a gatematerial on said oxide.
 11. A method comprising: exposing a dielectricdeposited on a substrate to a salt solution; and causing an oxide whichis different from said dielectric to form on said dielectric.
 12. Themethod of claim 11 including exposing said dielectric on said substrateto an aluminum salt solution.
 13. The method of claim 12 includingexposing said dielectric on said substrate to an aluminum chloridesolution.
 14. The method of claim 12 including exposing said dielectricon said substrate to an aluminum nitrate solution.
 15. The method ofclaim 12 including adjusting the pH of said aluminum salt solution. 16.The method of claim 12 wherein causing an oxide to deposit on saiddielectric includes causing reactants in said aluminum salt solution toreact with the top surface of said dielectric.
 17. The method of claim16 wherein causing said reactants in said aluminum salt solution toreact with the top surface of said dielectric includes depositing analuminum oxide layer ranging in thickness from about a few parts permillion to one or more atomic layers.
 18. The method of claim 11 whereinexposing said dielectric to said salt solution includes exposing adielectric selected from the group consisting of silicon dioxide,hafnium dioxide and zirconia to said salt solution.
 19. The method ofclaim 11 including removing said substrate from said salt solution andrinsing.
 20. The method of claim 11 wherein exposing said dielectric tosaid salt solution includes exposing said dielectric to said saltsolution for about a few seconds to about an hour.
 21. A methodcomprising: depositing a dielectric on a substrate using a first methodof deposition; and depositing an oxide on said dielectric by immersingsaid substrate in a salt solution, said deposition by immersingdifferent from said first method of deposition.
 22. The method of claim21 wherein depositing a dielectric on said substrate includes depositingan oxide on said substrate.
 23. The method of claim 22 whereindepositing said oxide on said substrate includes depositing hafniumoxide on said substrate.
 24. The method of claim 22 wherein depositingsaid oxide on said substrate includes depositing zirconia on saidsubstrate.
 25. The method of claim 22 wherein depositing said oxide onsaid substrate includes depositing silicon dioxide on said substrate.26. The method of claim 21 wherein causing an oxide to deposit on saiddielectric by immersing said substrate in a salt solution includescausing aluminum oxide to deposit on said dielectric by immersing saidsubstrate in an aluminum salt solution.
 27. The method of claim 26wherein causing said aluminum oxide to deposit on said dielectricincludes causing about a few parts per million of aluminum oxide to oneor more atomic layers of aluminum oxide to deposit on said dielectric.28. The method of claim 26 including adjusting the pH of said aluminumsalt solution.
 29. The method of claim 26 wherein causing aluminum oxideto deposit on said dielectric by immersing said substrate in saidaluminum salt solution includes causing the top surface of saiddielectric to react with reactants in said aluminum salt solution. 30.The method of claim 21 including forming a gate material on said oxide.31. The method of claim 21 wherein depositing a dielectric on asubstrate includes using a chemical vapor deposition technique todeposit said dielectric.
 32. A method comprising exposing asemiconductor substrate to a salt solution to form at least a portion ofa film on the surface of the substrate, the film or portion thereofincluding aluminum oxide as the primary film material.
 33. The method ofclaim 33 including adjusting the pH of the solution.
 34. The method ofclaim 32 including exposing said semiconductor substrate to an aluminumsalt solution.
 35. The method of claim 32 including depositing adielectric that is not aluminum oxide on the substrate before exposingthe substrate to the salt solution.